Purpose: We quantify the residual motion artifact in 4D-CT scan using the dynamic lung phantom which could simulate respiratory target motion and suggest a simple one-dimension theoretical model to explain and characterize the source of motion artifacts in 4DCT scanning.

Methods:we set-up regular 1D sine motion and adjusted three level of amplitude (10, 20, 30 mm) with fixed period (4s). The 4DCT scans are acquired in helical mode and phase information provided by the belt type respiratory monitoring system. The images were sorted into ten phase bins ranging from 0% to 90 %. The reconstructed images were subsequently imported into the Treatment Planning System for target delineation using a fixed contour window and dimensions of the three targets are measured along the direction of motion.

Results:Target dimension of each phase image have same changing trend. The error is minimum at 50% phase in all case(10, 20, 30 mm) and we found that ΔS(target dimension change) of 10, 20 and 30 mm amplitude were 0(0%), 0.1(5%), 0.1(5%) cm respectively compare to the static image of target diameter (2 cm). while the error is maximum at 30% and 80% phase ΔS of 10, 20 and 30 mm amplitude were 0.2(10%), 0.7(35%), 0.9(45%) cm respectively. Based on these result, we try to analysis the residual motion artifact in 4D-CT scan using a simple one-dimension theoretical model and also we developed a simulation program.

Conclusion:In this study, we focus on provides a more intuitive understanding about the residual motion artifact and try to explain the relationship motion parameters of the scanner, treatment couch and tumor. In conclusion, our results could help to decide the appropriate reconstruction phase and CT parameters which reduce the residual motion artifact in 4DCT.

Funding Support, Disclosures, and Conflict of Interest: This program was supported by the program of Basic Atomic Energy Research Institute (BAERI) which is a part of the Nuclear R and D programs (No. 20120004886) funded by the Ministry of Education, Science and Technology (MEST)